Protists are unicellular eukaryotes and dinoflagellates is a protist that is responsible for causing annual Florida red tides. When a large amount of dinoflagellates accumulates in the ocean they make the sea color red which is also called an algal bloom.
They also secrete a toxin that kills lots of aquatic animals. They are also toxic to other creatures like birds, humans. They come together to reproduce in a definite area therefore they accumulate together in large amounts causing red tides annually. Therefore the correct answer is dinoflagellates.
